Cheap benchtop power supplies are generally regarded as pieces of junk around these parts. They can measure well enough under perfect conditions, but when you use them a little bit, they fall over. There’s proof of this in hundreds of EEVblog posts, Amazon reviews, and stories from people who have actually owned these el-cheapo power supplies.
One of the guys who has had a difficult time with these power supplies is [Richard]. He picked up a MPJA 9616PS (or Circuit Specialists CSI3003SM) for a song. It quickly broke, and that means it’s time for a repair video. [Richard] is doing this one better – he has the 3A power supply, that sells for $55. With a stupidly simple modification, he upgraded this power supply to the 5A model that usually sells for $100.
The problem with [Richard]’s broken power supply were voltage and current adjustments knobs. This cheap power supply didn’t use rotary encoders – voltage and current were controlled by a pair of 1k and 10k pots. Replacing these parts cost about $5, and [Richard]’s power supply was back up on its feet.
After poking around inside this power supply, [Richard] noticed two blue trim pots. These trim pots were cranked all the way to the left, and by cranking them all the way to the right, the power supply could output 5 Amps. Yes, the 3A version of this power supply was almost identical to the 5A version, with the only difference being the price. It’s a good repair to a somewhat crappy but serviceable supply, but a great mod that puts a beefier power supply on [Richard]’s desk.